Table 4: Critical levels for protecting ecosystems
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| Contaminant and land use | Critical level | Averaging period | Additional requirements |
|---|---|---|---|
|
Sulphur dioxide: |
|||
|
30 µg/m3 |
Annual and winter average |
|
|
20 µg/m3 |
Annual and winter average |
|
|
10 µg/m3 |
Annual |
|
|
Sulphate particulate: |
|||
|
1.0 µg/m3 |
Annual |
Where ground-level cloud present > 10% of time |
|
Nitrogen dioxide |
30 µg/m3 |
Annual |
|
|
Ammonia |
8 µg/m3 |
Annual |
|
|
Ozone: |
|||
|
21,400 µg/m3-h |
6-month |
|
|
6420 µg/m3-h |
3-month |
|
|
6420 µg/m3-h |
3-month |
|
|
428 µg/m3-h |
5-day |
Mean daytime vpd below 1.5 kPa |
|
1070 µg/m3-h |
5-day |
Mean daytime vpd above 1.5 kPa |
|
|
Fluoride: |
|||
|
1.8 µg/m3 |
12-hour |
|
|
1.5 µg/m3 |
24-hour |
||
|
0.8 µg/m3 |
7-day |
||
|
0.4 µg/m3 |
|||
|
0.25 µg/m3 |
90-day |
||
|
3.7 µg/m3 |
12-hour |
|
|
2.9 µg/m3 |
24-hour |
||
|
1.7 µg/m3 |
7-day |
||
|
0.84 µg/m3 |
30-day |
||
|
0.5 µg/m3 |
90-day |
||
|
0.1 µg/m3 |
90-day |
Notes: Critical levels for nitrogen dioxide assume that either O3 or SO2 are also present at near guideline levels. Critical levels for ozone are expressed as a cumulative exposure over a concentration threshold referred to as AOT40 values (accumulative exposure over a threshold of 85.6 µg/m3, at 0°C), calculated as the sum of the difference between hourly ambient ozone concentrations and 85.6 µg/m3, when ozone concentrations exceed 85.6µg/m3). Ozone is only measured during daylight hours with a clear global radiation of 50 Wm-2 or greater; vpd = vapour pressure deficit.
